The present application relates to a read-only optical disc medium, and a method of fabricating the same. More specifically, the present application relates to a technique in which unique information can be separately provided to read-only optical disc media to be fabricated.
Examples of the related art include JP-A-2001-135021 (Patent Reference 1), WO 01/008145 (Patent Reference 2) and WO 02/101733 (Patent Reference 3).
For example, in playback only optical disc media, that is, ROM (Read Only Memory) optical disc media such as CDs (Compact Disc), DVDs (Digital Versatile Disc), BDs (Blu-ray disc (trademark)) and HD-DVDs (High Definition DVD), a lead-in area, a main data area and a lead-out area are formed on an optical disc from the inner track side to the outer track side.
Then, music, video, game, an application program, and the other information data are recorded in the main data area in accordance with a predetermined recording modulation mode. In addition, in the lead-in area, various items of management information are recorded including information for reproduction management of information data recorded in the main data area and physical information about a disc.
For example, many content holders use these read-only optical disc media as a means of providing contents because of low production costs due to excellent mass-productivity.
A DVD is taken as an example. The fabrication process steps of a read-only optical disc medium are roughly categorized into three processes: a mastering process in which an optical disc master is prepared with laser beams; a shaping and deposition process in which a stamper prepared from the optical disc master is used to produce a number of disc substrates and then a layer is formed on the disc substrates; and a bonding process in which two optical discs having a thickness of 0.6 mm, which make a pair, are bonded to each other with an adhesive having a predetermined thickness to form a DVD disc medium having a thickness of 1.2 mm.
The disc substrates mass-produced with the stamper in the shaping and deposition process have a convexo-concave patterns transferred from those formed on the stamper. In other words, on the portion to be the information recording surface, a record data string (embossed pit array) by pits and lands as a convexo-concave shape pattern is formed, and the record data string forms spiral or concentric recording tracks. On information recording surface on which pits and lands are formed, a metal alloy reflective layer is deposited on the convexo-concave shape.
After the disc is completed, laser light applied from a reproducing apparatus is reflected in the portions of pits and lands by the reflective layer.
It is not intended to additionally record information on the read-only optical disc after it is fabricated. In addition, as described above, a reflective layer is deposited on the information recording surface, but it is not considered to use the reflective layer as a recording layer.
Here, in recent years, in order to manage read-only optical discs on which a predetermined item of information data is recorded, such a method is demanded that additional information such as a unique ID number is recorded for every read-only optical disc to be fabricated.
However, in the read-only optical disc medium fabricated in accordance with the processes described above, it is difficult to record additional information with no influence on information data configured of an embossed pit array already formed.
On this account, in the modes proposed before in which additional information such as an ID number is recorded on a read-only optical disc, almost all of the modes have a premise that additional information is recorded in the area other than the information recording area (the lead-in area, the main data area and the lead-out area), or the modes adopt a scheme in which additional information is recorded in accordance with a mode different from a recording modulation mode of main signals (signals recorded with pits and lands transferred from a stamper).
However, in the read-only optical disc on which additional information is recorded in accordance with these schemes, the read-only optical disc has a premise that additional information data has signal output or the modulation mode different from that of the main signal, or that data is read out of the area other than the information recording area. Therefore, it is difficult to read data by a reproducing apparatus other than a reproducing apparatus having an exclusive read function, which causes the situations that it is difficult to read additional information by existing reproducing apparatuses, leading to a problem of poor compatibility.
For example, a BCA (Burst Cutting Area) defined by the DVD-ROM standards is recorded in the area on the inner track side than the lead-in area is provided in accordance with a recording modulation mode different from that of the main signal. On this account, it is necessary to use a reproducing apparatus having an exclusive read function.
In addition, Patent Reference 1 describes that an area other than an information recording area is selected in recording additional information.
Moreover, Patent Reference 2 discloses that in order to read the signals of recorded additional information, a reflectance difference is used between a portion on which existing information is recorded and an area on which additional information is recorded. In this case, it is necessary to use a reproducing apparatus having an exclusive read function.
In view of these situations, it is demanded that additional information is recorded in accordance with the same modulation mode as that of main signals in the information recording area formed of the lead-in area, the main data area and the lead-out area, that is, in the area in which information is recorded with an embossed pit array.